Ion sampling for APPI mass spectrometry

ABSTRACT

An atmospheric pressure ion source, e.g. for a mass spectrometer, that produces ions by atmospheric pressure photoionization (APPI). It includes a vaporizer, a photon source for photoionizing vapor molecules upon exit from the vaporizer, a passageway for transporting ions to, for example, a mass spectrometer system, and a means for directing the ions into the passageway. The center axis of the vaporizer and the center axis of the passageway form an angle that may be about  90  degrees. Included in the invention is a method for creating ions by atmospheric pressure photoionization along an axis and directing them into a passageway oriented at an angle to that axis.

RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 09/910,222 filed Jul. 20, 2001, which is acontinuation of U.S. patent application Ser. No. 09/204,213 filed Dec.2, 1998 (now U.S. Pat. No. 6,294,779, issued Sep. 25, 2001), which is acontinuation of U.S. patent application Ser. No. 09/030,676 filed Feb.25, 1998 (now U.S. Pat. No. 6,278,110, issued Aug. 21, 2001), which is acontinuation of U.S. patent application Ser. No. 08/794,248 filed Feb.3, 1997 (now U.S. Pat. No. 5,750,988, issued May 12, 1998), which is acontinuation of U.S. patent application Ser. No. 08/555,250, nowabandoned, which is a continuation-in-part of U.S. patent applicationSer. No. 08/273,250 filed Jul. 11, 1994 (now U.S. Pat. No. 5,495,108,issued Feb. 27, 1996).

FIELD OF THE INVENTION

[0002] The present invention relates to a method and apparatus forobtaining improved signal relative to noise without loss of ioncollection efficiency for use in mass spectrometry, including liquidchromatography/mass spectrometry, especially as regards to the techniqueof generating analyte ions known as atmospheric pressure photoionization(APPI).

BACKGROUND INFORMATION

[0003] Liquid chromatography and mass spectrometry have proven powerfulanalytical tools in identifying molecular components of our world.Liquid chromatography is a fundamental separation technique. Massspectrometry is a means of identifying “separated” components accordingto their characteristic “weight” or mass-to-charge ratio. The liquideffluent from liquid chromatography is prepared for ionization andanalysis using any of a number of techniques. A conventional technique,atmospheric pressure ionization-electrospray (or simply “electrospray”,for short), involves spraying the sample into fine droplets.

[0004] Early systems which employed electrospray liquidchromatography/mass spectrometry techniques utilized flow splitters thatdivided the high performance liquid chromatography column effluent. As aresult of the effluent splitting, only a small portion, typically 5-50micro liters per minute, was introduced into the “spray chamber”. Thebulk of the column effluent did not enter the spray chamber, but wentdirectly to a waste or fraction collector. Because electrospray/massspectrometry generally provides a concentration sensitive detector, itwas not necessary to analyze the entire column effluent flow to obtainsensitive results. Results obtained by splitting are comparable insensitivity to those obtained by introduction of the entire columneffluent flow into the spray chamber (assuming equal charging andsampling efficiencies). Such low flow rates enabled generation of anelectrosprayed aerosol solely through the manipulation of electrostaticforces. However, the use of flow splitters has performed poorly in thatthey experience plugging problems and poor reproducibility.

[0005] Newer electrospray systems generate a charged or ionized aerosolthrough the combination of electrostatic forces and some form ofassisted nebulization. Nebulization is the process of breaking a streamof liquid into fine droplets. Nebulization may be “assisted” by a numberof means, including but not limited to pneumatic, ultrasonic or thermalassists. The assisted nebulization generates an aerosol from the highperformance liquid chromatography column effluent, while electric fieldsinduce a charge on the aerosol droplets. The charged aerosol undergoesan ion evaporation process whereby desolvated analyte ions are produced.Ideally, only the desolvated ions enter the mass spectrometer foranalysis.

[0006] It is a desired feature of an assisted nebulizer system that thevacuum system leading to the mass spectrometer permit desolvated ions toenter, but do not permit relatively large solvated droplets present inthe electrosprayed aerosol to enter. Several design approaches arecurrently in use, but none of the assisted nebulization methodscurrently practiced provide reliable sensitivity along with robustinstrumentation.

[0007] In conventional electrospray/nebulization mass spectrometrysystems, the electrosprayed aerosol exiting from the nebulizer issprayed directly towards the sampling orifice or other entry into thevacuum system. That is, the electrosprayed aerosol exiting from thenebulizer and entry into the vacuum system are located along a commoncenter axis, with the nebulizer effluent pointing directly at the entryinto the vacuum system and with the nebulizer being considered to belocated at an angle of zero (0) degrees relative to the common centeraxis.

[0008] One conventional approach directed at improving performanceadjusts the aerosol to spray “off-axis”. That is, the aerosol is sprayed“off-axis” at an angle of as much as 45 degrees with respect to thecenter axis of the sampling orifice. In addition, a counter current gasis passed around the sampling orifice to blow the solvated droplets awayfrom the orifice. The gas velocities typically used generate a plume ofsmall droplets. Optimal performance appears to be limited to a flow rateof 200 microliters per minute or lower.

[0009] In another system, an aerosol is generated pneumatically andaimed directly at the entrance of a heated capillary tube. The heatedcapillary exits into the vacuum system. Instead of desolvated ionsentering the capillary, large charged droplets are drawn into thecapillary and the droplets are desolvated while in transit. Theevaporation process takes place in the capillary as well. Exiting thecapillary in a supersonic jet of vapor, the analyte ions aresubsequently focused, mass analyzed and detected.

[0010] This system has several disadvantages and limitations, includingsample degradation, re-clustering, and loss of sensitivity. Sensitivesamples are degraded due to the heat. In the supersonic jet expansionexiting the capillary, the desolvated ions and vapor may recondense,resulting in solvent clusters and background signals. While theseclusters may be re-dissociated by collisionally induced processes, thismay interfere in identification of structural characteristics of theanalyte samples. The large amount of solvent vapor, ions and dropletsexiting the capillary require that the detector be arrangedsubstantially off-axis with respect to the capillary to avoid noise dueto neutral droplets striking the detector. Removing the large volume ofsolvent entering the vacuum system requires higher capacity pumps.

[0011] Still another conventional system generates the electrosprayedaerosol ultrasonically, uses a counter current drying gas, and mosttypically operates with the electrosprayed aerosol directed at thesampling capillary. One disadvantage of this configuration is thatoptimal performance is effectively limited to less than five hundred(500) microliters per minute. Adequate handling of the aqueous mobilephase is problematic. Furthermore, the apparatus is complex and prone tomechanical and electronic failures.

[0012] In another conventional system, a pneumatic nebulizer is used atsubstantially higher inlet pressures (as compared with other systems).This results in a highly collimated and directed electrosprayed aerosol.This aerosol is aimed off axis to the side of the orifice and at thenozzle cap. Although this works competitively, there is still some noisewhich is probably due to stray droplets. The aerosol exiting thenebulizer has to be aimed carefully to minimize noise while maintainingsignal intensity. Thus, repeated and tedious adjustments are oftenrequired.

[0013] In addition to atmospheric pressure ionization-electrospray,another conventional technique for preparing a liquid effluent forionization and analysis is atmospheric pressure chemical ionization.Fundamentally, atmospheric pressure chemical ionization involves theconversion of the mobile phase and analyte from the liquid to the gasphase and then the ionization of the mobile phase and analyte molecules.Atmospheric pressure chemical ionization is a soft ionization techniquethat yields charged molecular ions and adduct ions. Atmospheric pressurechemical ionization actually includes several distinct ionizationprocesses, with the relative influence of each process dependent on thechemistry of the mobile phase and the analyte.

[0014] Each of techniques of atmospheric pressureionization-electrospray and atmospheric pressure chemical ionization issuited to different, and complementary, classes of molecular species.Briefly, atmospheric pressure ionization-electrospray is generallyconcentration dependent (that is to say, higher concentration equalsbetter performance), and performs well in the analysis of moderately tohighly polar molecules. It works well for large, biological moleculesand pharmaceuticals, especially molecules that ionize in solution andexhibit multiple charging. Atmospheric pressure ionization-electrosprayalso performs well for small molecules, provided the molecule is fairlypolar. Low flow rates enhance the performance of the atmosphericpressure ionization-electrospray technique. Atmospheric pressurechemical ionization, on the other hand, performs with less dependence onconcentration and performs better on smaller non-polar to moderatelypolar molecules. Higher flow rates enhance the performance of theatmospheric pressure chemical ionization technique. However, there arestill analytes that do not ionize at all when these ionizationtechniques are employed, or which ionize weakly when these ionizationtechniques are employed.

[0015] In addition to the two conventionally employed ionizationtechniques of atmospheric pressure ionization-electrospray andatmospheric pressure chemical ionization, an alternative technique whichhas been developed for producing ions from a liquid sample is referredto as atmospheric pressure photoionization (APPI). Generally, thetechnique of atmospheric pressure photoionization provides a method ofanalyzing a sample of an analyte provided as a sample solution.According to one such technique, the sample solution is formed into anaerosol spray, for example in a nebulizer, and the solvent isevaporated. The sample stream is irradiated, e.g., subjected to photons,in a region at atmospheric pressure, in the vapor state afterevaporation of the sprayed droplet. Collisions between the photons andthe analyte result in ionization of the analyte. The analyte ions arepassed from the atmospheric pressure ionization region into a massanalyzer for mass analysis.

[0016] According to another such technique, dopant is provided, eitherseparately or as the solvent of the sample solution. The sample solutionis formed into a spray, for example in a nebulizer, and the solvent isevaporated. The sample stream is irradiated, e.g., subjected to photons,in a region at atmospheric pressure to ionize the dopant. Again, thisirradiation step takes place when the sample is in the vapor state afterevaporation of the sprayed droplet. Then subsequent collisions betweenthe ionized dopant and the analyte result in ionization of the analyte.Analyte ions are passed from the atmospheric pressure ionization regioninto a mass analyzer for mass analysis. This technique has been found togive enhanced ionization for some substances, as compared to atmosphericpressure chemical ionization.

[0017] Configurations for APPI in present use often provideunsatisfactory signal relative to noise and do not provide for optimalion collection efficiency. Therefore, there exists a need for animproved method and apparatus for obtaining improved signal relative tonoise without loss of ion collection efficiency for use in massspectrometry, including liquid chromatography/mass spectrometry,especially as regards the technique of generating analyte ions known asatmospheric pressure photoionization.

SUMMARY OF THE INVENTION

[0018] The invention comprises an atmospheric pressure ion source, e.g.for a mass spectrometer, that produces ions by atmospheric pressurephotoionization (APPI). It includes a vaporizer, a photon source forphotoionizing vapor molecules upon exit from the vaporizer, a passagewayfor transporting ions to, for example, a mass spectrometer system, and ameans for directing the ions into the passageway. In one embodiment, thepassageway has a center axis situated substantially orthogonal to thecenter axis of the vaporizer. In another embodiment, the center axis ofthe passageway

[0019] and the center axis of the vaporizer define an angle in the rangeof about 20 degrees to 180 degrees.

[0020] Included in the invention is a method for creating andtransporting ions in an atmospheric pressure ion source by forming themwith atmospheric pressure photoionization along an axis and directingthem into a passageway oriented at an angle to that axis.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a diagram that illustrates an apparatus for employingthe atmospheric pressure ionization-electrospray technique, according toone embodiment of the present invention.

[0022]FIG. 2 is a diagram that illustrates an alternate embodiment of anapparatus for employing the atmospheric pressure ionization-electrospraytechnique, according to the present invention.

[0023]FIG. 3 is a diagram that illustrates an alternate embodiment of anapparatus for employing an atmospheric pressure ionization-electrosprayapparatus, according to the present invention.

[0024]FIG. 4 is a diagram that illustrates an alternate embodiment of anapparatus for employing the atmospheric pressure ionization-electrospraytechnique, according to the present invention.

[0025]FIG. 5 is a diagram that illustrates an apparatus for employingthe atmospheric pressure chemical ionization technique, according to oneembodiment of the present invention.

[0026]FIG. 6 is a diagram that illustrates an apparatus for employingthe atmospheric pressure photoionization technique, according to oneembodiment of the present invention.

[0027]FIG. 7 is a diagram that illustrates an apparatus for employingthe atmospheric pressure photoionization technique, according to anotherembodiment of the present invention.

[0028]FIG. 8 is a diagram that illustrates an apparatus for employingthe atmospheric pressure photoionization technique, according to stillanother embodiment of the present invention.

[0029]FIG. 9 is a diagram that illustrates a vaporizer for use in anapparatus for employing the atmospheric pressure photoionizationtechnique, according to another embodiment of the present invention.

[0030]FIG. 10 is a diagram that illustrates an apparatus for employingthe atmospheric pressure photoionization technique, according to stillanother embodiment of the present invention.

[0031]FIG. 11 is a diagram that illustrates a mass spectrometer systemthat incorporates an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0032]FIG. 1 depicts an apparatus 10 configured according to oneembodiment of the current invention. As in conventional sampleintroduction, a liquid sample is conducted through a nebulizer and intoa first passageway 14, exiting via a second orifice 15 (the exit of thefirst passageway 14) under conditions which create a vapor of chargeddroplets or electrosprayed aerosol 11. This embodiment of the inventionprovides a rather different electrospray particle transport as comparedwith conventional electrospray processes. FIG. 1 depicts the transportof the electrospray droplets from the exit 15 of the first passageway14, through the distance to the opening or orifice 17 of a secondpassageway 22, and entering the second passageway 22 where theorientation angle θ of the center axis of the exiting electrosprayedaerosol 11 and the center axis of the second passageway 22 is between 75and 105 degrees with respect to each other. The angle may be greaterthan 105 and, in principle, as great as 180 degrees; in practice, bestresults have been obtained at settings at or near 90 degrees. As shownin FIG. 1, the angle θ defines the location of the first passageway 14,that is, the nebulizer or other source of electrosprayed aerosol 11,relative to the second passageway 22, that is, the entry into the vacuumsystem. The angle θ is considered to be zero (0) degrees when the exit15 for the electrosprayed aerosol 11 and the center axis of the firstpassageway 14 are pointing directly at the entrance 17 and the centeraxis of the second passageway 22. The angle θ is considered to be 180degrees when the exit 15 for the electrosprayed aerosol 11 and thecenter axis of the first passageway 14 are pointing directly away fromthe entrance 17 and the center axis of the second passageway 22.

[0033] The charged droplets forming the electrosprayed aerosol areelectrostatically attracted laterally across a gap between the exit 15of the first passageway 14 into the opening 17 of the second passageway22. The electrostatic attraction is generated by attaching voltagesources to components of the apparatus. A first voltage source (notshown) is connected to a housing 16 which houses the second passageway22. The housing 16 is not necessarily an enclosure but may be any shapethat can act as a guide for the ions and can support fluid dynamics of adrying gas (discussed below). A second voltage source (not shown) isconnected to the second passageway 22. The first passageway 14 isgenerally kept at ground potential.

[0034] In the course of crossing the gap and approaching the opening 17to the second passageway 22, especially after passing through an opening21 in the housing 16 containing the second passageway 22, theelectrosprayed aerosol is subjected to the cross flow of a gas 20—acondition that operates to remove solvent from the droplets, therebyleaving charged particles or ions. The ions are amenable to analysis byoperation of an analytic instrument capable of detecting and measuringmass and charge of particles such as a mass spectrometer (not shown).The second passageway 22 exits into the mass spectrometer or equivalentinstrument.

[0035] A standard electrospray mass spectrometry system with a pneumaticnebulizer provides the base structure. A spray box 12 (see FIG. 5) ofplexiglass or some other suitable material for preventing shock andcontaining noxious vapors replaces the standard spray chamber. Withinthe spray box 12, the nebulizer and first passageway 14 may be arrangedin a variety of configurations, so long as the distances between theseparate high voltage sources are sufficient to prevent discharges.Additional surfaces at high voltage may be used to shape the electricalfields experienced by the electrosprayed aerosol. In the embodimentdepicted in FIG. 1, the system includes a drying gas 20 to aiddesolvation and prevent droplets in the electrosprayed aerosol 11 fromentering the orifice 17 of the second passageway 22 and the vacuumsystem (not shown). An alternate embodiment may include a heatedcapillary as the second passageway 22 in an internal source off-axisgeometry, such that the capillary is off-axis with respect to quadrupoleand detector components.

[0036] The positive ion configuration shown in FIG. 1 typically has thesecond voltage source set approximately at 4.5 kV, the first voltagesource at −4 kV, and the first passageway 14 (wherein the passageway iscomprised of a needle) set at relative ground. Gas, usually nitrogen atnominally 200 to 400 degrees Centigrade and approximately ten standardliters per minute, is typically used as a cross flow drying gas,although other gases can be used. The drying gas 20 flows across theaperture at approximately 90 degrees to the axis of the charged moleculein the electrosprayed aerosol.

[0037] The term “passageway”, as used herein with respect to the secondpassageway, means “ion guide” in any form whatsoever. It is possiblethat the passageway is of such short length relative to the openingdiameter that it may be called an orifice. Other ion guides, includingcapillaries, which are or may come to be used, can operate in theinvention. The configuration herein are not meant to be restrictive, andthose skilled in the art will see possible configurations notspecifically mentioned here but which are included in the teaching andclaims of this invention.

[0038]FIG. 5 illustrates the inventive apparatus as embodying andconfigured for atmospheric pressure chemical ionization. As can readilybe observed by even a quick perusal of the FIG. 1 and FIG. 5 set side byside, the invention provides that embodiments for atmospheric pressureionization-electrospray and atmospheric pressure chemicalionization—share much of the same hardware. It is apparent to one ofaverage skill in the art that the configurations depicted herein, aswell as many suggested by the illustrative examples, can be adoptedinterchangeably with relatively straightforward modification ofinput/output interfaces. FIG. 5 references elements common to FIG. 1through use of the same numerical identification. By way of background,the conventional atmospheric pressure chemical ionization technique is amulti-step process involving the steps of:

[0039] 1) nebulization of the mobile phase and analyte (breaking intodroplets);

[0040] 2) vaporization of the droplets;

[0041] 3) ionization of the mobile phase molecules by electrons from thecharge source generating a corona discharge;

[0042] 4) ionization of the analyte molecules by the mobile phase ions.

[0043]FIG. 5 depicts an apparatus 100 configured according to thecurrent invention. The sample is nebulized (not shown) by any of numberof known nebulization methods, and the resultant droplets proceed intoand through a vaporizer 110. The vaporizer 110 is formed by a capillaryor other tube-like structure 120 composed of glass or ceramic or othersuitable material. The tube-like structure 120 is subjected tocontrolled heating through close association with a heating device 130.In both the tube-like structure 120 and the heating device 130 are of alength of several or more inches, the length being determined by theextent to which the heating device 130 is effectively insulated and,being insulated, how effectively the conditions in the vaporizerinterior 135 promote ionization of the solvent molecules.

[0044] The vaporizer exit 140 allows the vaporized solvent and analytein the aerosol to pass into an intervening space or gap 145. Themolecules typically form a corona (not depicted) at this stage. Becausethe vaporizer is typically at ground potential, the exiting molecules“sees” a relatively large charge (either negative or positive) from acharge source 150. The charge source 150 is a charged point (a needle)in the preferred embodiment and the charge source is positioned so as tooptimally induce charge transfer among the molecules collected in thegap 145. At this point, atmospheric pressure chemical ionization takesplace. The charged point creates a corona discharge in the ambientnitrogen atmosphere. The hot jet of gas from exit (140), composed ofsolvent molecules and analyte molecules, enters the corona dischargeregion, wherein some of the molecules are ionized. Ionization processesinclude electron impact ionization and charge transfer reactions (alsocalled chemical ionization). The ions are attracted toward the secondpassageway due to the electric fields created by the voltages applied tovarious components of the system. In the embodiment shown, the analyteions are electrostatically attracted to a complementary (either positiveor negative) charge from a voltage source (not shown) applied to thehousing 16 of a second passageway 22 which leads to the mass analyzer(not shown) and a stronger relative charge from a voltage source (notshown) applied to the second passageway 22 itself, thereby attractingthe analyte ions into the second passageway 22 through the opening 17thereto.

[0045] The orientation angle 0 defining the location of the vaporizerexit 140 relative to the second passageway 22 is between 75 and 105degrees. The angle may be greater that 105 degrees; in principle, it maybe as great as 180 degrees. However, best results have been obtained atangles at or near 90 degrees. As shown in FIG. 5, the angle θ, whichdefines the location of the vaporizer exit 140, is measured with respectto the center axis defined by the second passageway 22, that is, theentry into the vacuum system. The angle θ is considered to be zero (0)degrees when the vaporizer exit 140 and the center axis of the vaporizer110 are pointing directly at the entrance 17 and the center axis of thesecond passageway 22. The angle θ is considered to be 180 degrees whenthe vaporizer exit 140 and the center axis of the vaporizer 110 arepointing directly away from the entrance 17 and the center axis of thesecond passageway 22. The vaporizer 110 is generally kept at groundpotential.

[0046] In one embodiment the atmospheric pressure chemical ionizationaccessory accomplishes nebulization as mobile phase and analyte aresprayed out of a small needle. The concentric flow of nebulizing gastears the stream of liquid into fine droplets in the aerosol. A heatedtube in the atmospheric pressure chemical ionization accessory vaporizesthe droplets of mobile phase and analyte as the droplets pass throughthe tube. The temperature of the tube is adjustable relative to thevolatility of the mobile phase (low volatility indicates need for highertemperature). The selected temperature must substantially completevaporization without thermally degrading the analyte.

[0047] After being vaporized, the mobile phase molecules ionize andsubsequently react with and ionize the analyte molecules. The analyteions thus produced are subject to the separation and direction affordedby the invention as taught herein.

EXAMPLES

[0048] A number of different configurations have been proven possible.Examples of certain tested configurations follow:

[0049]FIG. 2 shows a configuration of the invention in which a thirdvoltage source, a plate 24, is positioned beside the exit 15 of thefirst passageway 14 and distal to the side near to which the firstvoltage source, the opening 21 in the housing 16, and the opening 17 tothe second passageway 22 are positioned. The plate 24 runs a positivevoltage relative to the charge on the housing 16. Experiments show theelectrosprayed aerosol “sees” a mean voltage between the plate 24 andthe charged housing 16. Results suggest that the repeller effect may becaptured and ion collection yield increased by careful sculpting of boththe electric field and the gas flow patterns.

[0050]FIG. 3 shows a two-voltage source system as in FIG. 2 with theaddition of a grounded spray chamber 26. The spray chamber 26 operatesto contain the electrosprayed aerosol and route condensed vapor towaste.

[0051]FIG. 4 shows the addition of a ring-shaped electrode 28 encirclingthe electrosprayed aerosol exiting from the needle or first passageway14 at ground, with all of the elements configured as in FIG. 3. Thering-shaped electrode 28 induces a charge in the droplets by virtue ofthe potential difference in charge between the droplets and thering-shaped electrode 28. Other potentials in the system can be used todirect the sampling of ions.

[0052]FIG. 5 illustrates an atmospheric pressure chemical ionizationembodiment of the invention taught herein. The typical relative voltagesare: source 150 set at between 1.2 kV and 2 kV; the surface of thehousing 16 immediately adjacent to the entrance to the second passageway22 set at approximately 3.5 kV; and the second passageway 22 set at aslightly greater charge of about 4 kV (both the surface of the housing16 and the second passageway 22 oppositely charged from charge of thesource 150). The delta voltage ranges from between about 4 to 6 kV.

[0053] The present invention, according to another example embodimentthereof, relates to a method and apparatus for obtaining improved signalrelative to noise without loss of ion collection efficiency for use inmass spectrometry, including liquid chromatography/mass spectrometry, asregards the technique of generating analyte ions known as atmosphericpressure photoionization. FIG. 6 illustrates an apparatus 100 configuredaccording to one example embodiment of the present invention. Avaporizer 110 includes a first passageway 120, such as a capillary orother tube-like structure, composed of glass or ceramic or othersuitable material. The first passageway 120 has an inlet orifice 120 a,a center axis 120 b, an interior vaporizer 120 c through which a solutesample 101 may pass and in which the solute sample 101 is vaporized, andan exit orifice 120 d.

[0054] According to one embodiment of the present invention, the firstpassageway 120 is configured to be heated by a heating device 130(details not shown). The length of both the first passageway 120 and theheating device 130 are determined by the extent to which the heatingdevice 130 is effectively insulated and, being insulated, howeffectively the conditions in the interior vaporization chamber 120 cpromote vaporization of the solvent molecules in the solute sample.Immediately after the exit orifice 120 d of the first passageway 120 ofthe vaporizer 110, is an intervening space 145. Vaporized molecules ofthe solute sample 101 pass through the exit orifice 120 d into theintervening space 145.

[0055] Although a center axis 120 b has been described as related to thestructure of the vaporizer and of the first passageway 120, it should beunderstood more broadly. Vaporized molecules of the solute sample 101pass through the exit orifice 120 d in a spray that is approximatelycentered on an axis herein called the molecular axis (not shown in FIG.7). In FIG. 6, the molecular axis is approximately coincident with thecenter axis 120 b of the vaporizer 120. It is possible to constructvaporizers for which the molecular axis is not coincident with a centeraxis of the vaporizer. In the invention, the direction of the spray ofvaporized molecules is the direction that should be combined with otheraxes to form claimed angles. Thus, the term “center axis of thevaporizer” should be given the interpretation of the molecular axis whenthe molecular axis and what might be considered as a center axis of thevaporizer are not coincident.

[0056] Positioned adjacent to first passageway exit orifice 120 d is aphoton source 150, such as a ultraviolet (UV) lamp. According to oneexample embodiment of the present invention and as employed in thevarious example embodiments shown herein, the photon source 150 is avacuum ultraviolet (VUV) lamp configured to generate ultravioletradiation having a wavelength of less than 200 nm. The photon source 150is configured to generate photons and direct them into the interveningspace 145 at the molecules that pass through the exit orifice 120 d ofthe vaporizer 110. It is intended that the wavelengths of the photonsand the placement of the photon source be such as to photoionize vapormolecules that have passed through the exit orifice 120 d into theintervening space 145. Advantageously, the photon wavelengths may bechosen to maximize production of analyte ions relative to ions ofsolvent molecules, but such a choice is not necessary to the invention.Also in some cases, the wavelengths can be chosen to maximize ionizationof a dopant, which may be the solvent and which then ionizes theanalyte.

[0057] According to one example embodiment of the present invention, thephoton source 150 is situated generally opposite to an inlet orifice 17of a second passageway 22 (discussed in greater detail below), andpointing toward the intervening space 145. In accordance with alternateexample embodiments, the photon source 150 is instead situated so as tobe positioned to one side (e.g., not opposite) of the inlet orifice 17,or almost anywhere on a sphere surrounding inlet orifice 17 (with dueregard for other structures such as the vaporizer 110, but so as tostill furnish photons that intersect the vaporized sample in theintervening space 145. Irrespective of the arrangement employed, it ispreferred that the photon source 150 be placed relatively close to theionization area to maximize the photon flux and ionization rate. FIG. 9illustrates still another example embodiment of the present invention,whereby a photon source 550 is provided within a vaporizer 510 so as tocause ionization of the analyte molecules prior to the molecules exitingthrough the exit orifice 520 d of the vaporizer 510. Yet another exampleembodiment is illustrated in FIG. 10, where the vapor stream fromvaporizer 610 flows through the photon source 650 and analyte moleculesare photoionized in a region 657 surrounded by that photon source.

[0058] As mentioned above, a second passageway 22 (see FIG. 6), such asa capillary tube, has an inlet orifice 17, a center axis 22 a, and anexit 22 b which may be, as mentioned previously, connected to or exitinto a mass spectrometer. The center axis 120 b of the first passageway120 and the center axis 22 a of the second passageway 22 define an angletherebetween that is in the range of about 20 degrees to 180 degrees. Inone embodiment of the invention, e.g., as illustrated in FIG. 6, theangle is convenient at about 90 degrees or greater. The definitions ofzero (0) and 180 degrees are as above.

[0059] One property of the angle between the center axis 120 b and thecenter axis 22 a, as contrasted with zero (0) angle, is thatunevaporated material, e.g., solvent droplets, does not enter the secondpassageway 22. When used to furnish ions to a mass spectrometer, thisproperty can result in less “noise” and thus higher sensitivity fordetection of analyte samples.

[0060] Another property of the angle between the center axis 120 b andthe center axis 22 a is the resulting flexibility in location of thephoton source 150. The photon source 150 can be arranged to irradiatethe vapor after it exits the vaporizer 110 and thus where thevaporization is more complete than within the vaporizer itself. Manysuch arrangements of the photon source 150 are now possible. The resultcan be a larger number of analyte ions produced, again leading to highersensitivity for detection of analyte samples when the ion source is usedwith a mass spectrometer.

[0061] In the present invention, the lower limit of the angle defined bythe center axis 120 b of the vaporizer and the center axis 22 a of thesecond passageway is about 20 degrees and is determined by theconsideration that two advantages of the configuration of the inventionbegin to disappear at small angles. Thus, as the angle decreases, moresolvent droplets enter the second passageway 22 and also it becomes moredifficult to place the photon source 150 advantageously. Angles greaterthan 60 degrees are generally more satisfactory than smaller angles, andperformance often is better yet with angles of about 90 degrees orgreater.

[0062] The configuration and arrangement of the vaporizer and the secondpassageway can be such that the center axis 120 b of the vaporizer andthe center axis 22 a of the second passageway do not intersect, that is,the two axes may not lie in the same plane. In those cases, the anglemay be defined geometrically by drawing a line connecting the two axessuch that the line is orthogonal to each, then displacing one axisparallel to itself along that line until the other axis is intersected.The angle is then defined as described above.

[0063] As previously mentioned, the term “passageway”, as used hereinmeans “ion guide” in any form whatsoever. The term should be consideredto include any physical structure required for creating a passage forthe transport of ions. It is possible that the second passageway 22 isof such short length relative to the opening diameter of the inletorifice 17 that the second passageway 22 may be called an orifice. Inthat case, center axis 22 a may be along the direction of the normal tothe plane of the orifice. Other “ion guides” which are, or may come tobe, used can operate in the invention. The use of the term “passageway”is not intended to limit the scope of the present invention.

[0064]FIG. 6 also illustrates a means for generating an electric field.The electric field means is employed to direct the ionized moleculesfrom the intervening space 145 into the inlet orifice 17 of the secondpassageway 22. It is noted that one advantage of using the atmosphericpressure photoionization technique is that, unlike the electrosprayionization and atmospheric pressure chemical ionization techniques, itdoes not employ an electric field in the ion production process.Electrospray ionization and atmospheric pressure chemical ionizationtechniques use electric fields to help generate ions. As a result, thefeasible voltage and electrode configurations employed by thesetechniques are limited by the requirement that electric fields must beof appropriate magnitudes and shapes for use in the ion production. Bycontrast, the voltage and electrode configurations in the atmosphericpressure photoionization technique are not required to produce electricfields for the ionization process. Instead, the atmospheric pressurephotoionization technique of the present invention advantageouslyemploys an electric field means to merely move the ions created by thephotons to the desired location, e.g., to the inlet orifice 17 of thesecond passageway 22. The electric field means does not have theadditional requirement of having to assist in ionization of the analytesample.

[0065] In the atmospheric pressure photoionization technique of thepresent invention, there are various conceivable configurations by whichan electric field may be established in order that ions are directedtowards the inlet orifice 17 of the second passageway 22 and into a massspectrometer. In the embodiment illustrated in FIG. 6, the electricfield means includes a first voltage source 103 and a second voltagesource 104 that are coupled to electrodes to generate an electric field.The first voltage source 103 is coupled to the first passageway 120 ofthe vaporizer 110 and the second voltage source 104 is coupled to thesecond passageway 22, such that an electric field is established betweenthe exit orifice 120 d of the first passageway 120 and the inlet orifice17 of the second passageway 22. The shape of the electric field soestablished is determined by the exact configurations and placements ofthe electrodes (e.g., the first passageway and the second passageway)and their surroundings. The shape and magnitude of the electric fieldgenerated by the voltage sources 103 and 104 are such as to cause thefield to move and direct the ionized molecules from the interveningspace 145 into the inlet orifice 17 of the second passageway 22.

[0066] The term “voltage source” should be interpreted broadly. Avoltage source, for example, need not be an actual electrical powersupply. It might, for example, be simply a connection to ground,establishing a ground potential (commonly called zero voltage), or toanother conductor at a definite potential. An electric field is createdby a potential difference between conductors or electrodes. For a givenpotential difference or set of potential differences, the field is thesame regardless of the absolute potentials. A “voltage source”, as theterm is used herein, is anything that establishes the potential onwhatever it is connected to. In the example embodiment of FIG. 6, thefirst passageway 120 can be at or about ground potential (within about300 V of zero) and the second passageway 22 can be at a high negativepotential, or the first passageway 120 can be at high positive potentialand the second passageway 22 at or about ground. (The polarities givenare for positive ions.) All conductors and electrodes in the ion sourceare connected to voltage sources so that they have establishedpotentials. Although operation of the ion source with one or more“floating” electrodes is possible, it is usually not preferred.

[0067] Of course, the means for generating an electric field is notlimited to a pair of voltage sources coupled to respective passageways.For instance, according to an example embodiment (and as illustrated asan optional feature in FIG. 6), an auxiliary electrode 152 connected toa voltage source (not shown) is provided that establishes an electricfield between it and the second passageway 22 to assist motion of ionsinto the latter. According to another example embodiment (and asillustrated as an optional feature in FIG. 6), a lamp electrode 153connected to a voltage source (not shown) is provided and is positionedso as to surround the photon source 150, thereby establishing anelectric field between the inlet orifice 17 of the second passageway 22and the lamp electrode 153. According to another example embodiment, thevaporizer 110 may be employed as an electrode. According to stillanother embodiment and as illustrated in FIG. 9, a photon source 550 ispositioned in a vaporizer 510 such that ions are formed internal to thevaporizer 510, and the exit orifice 520 d of the vaporizer 510 isemployed as an electrode to establish an electric field relative to theinlet orifice of a second passageway. Furthermore, it is noted thatwhile embodiments have been described herein having two electrodescoupled to respective voltage sources, alternative embodiments of thepresent invention may employ one or more electrodes coupled to a voltagesource, and one or more electrodes coupled to or maintainedsubstantially at ground, e.g., at ground or near ground. Alternatively,the electric field means may include a single voltage source having aresistive divider, or any other conceivable arrangement that is capableof generating an electric field for directing ionized molecules from theintervening space 145 into the inlet orifice 17 of the second passageway22.

[0068] As mentioned above, according to a preferred embodiment, theatmospheric pressure photoionization technique employs as the electricfield means an electrode plate around the photon lamp (also referred toas a “lamp electrode”) to establish the electric field relative to theinlet orifice 17 of the second passageway 22. An example of such a lampelectrode is illustrated as lamp electrode 153 in FIG. 6. Preferably,according to this embodiment, the second passageway 22 is maintained ata high voltage (e.g., −1500 to −6000 Volts for the positive ion and+1500 to +6000 Volts for the negative ion), while the vaporizer 110 andthe lamp electrode 153 are coupled to ground. However, it is recognizedthat, in accordance with other example embodiments, this arrangementcould be reversed such that the potential of the second passageway isnear or at ground while the vaporizer and the lamp electrode aremaintained at the specified, or other predetermined, voltages.

[0069] In operation, according to the example embodiment of the presentinvention illustrated in FIG. 6, a liquid solute sample 101, which iscomprised of a solvent and an analyte and which may be in the form of anaerosol, proceeds through the first passageway 120 of the vaporizer 110.The aerosol within the first passageway 120 is heated by the heatingdevice 130 in order to promote vaporization of the aerosol. Thevaporized molecules exit the first passageway 120 of the vaporizer 110through the first passageway exit 120 d and into the intervening space145. The vapor molecules exiting from first passageway exit 120 d aresubjected to photons generated by the photon source 150. The interactionof the photons from the photon source 150 with the vapor moleculescauses ionization of the analyte. Once formed, the analyte ions aremoved and directed by the electric field generated by the electric fieldmeans into the second passageway 22 through the opening 17. The analyteions pass through the second passageway 22 into a mass analyzer (notshown), such as a mass spectrometer, in order to be analyzed.

[0070]FIG. 7 illustrates an apparatus 200 configured according toanother example embodiment of the present invention. In this embodiment,a nebulizer 302 is configured to receive via its inlet a solute sample301. The nebulizer 302 is coupled to a vaporizer 310. The vaporizer 310includes a first passageway 320 that has an inlet orifice 320 a, acenter axis 320 b, an interior vaporization chamber 320 c and an exitorifice 320 d. The first passageway 320 is configured to be heated by aheating device 330 to promote vaporization of the solvent molecules. Atthe end of the first passageway 320 of the vaporizer 310 is anintervening space 345.

[0071] Positioned adjacent to first passageway exit 320 d is a photonsource 350, such as a UV lamp. As discussed above, according to oneexample embodiment of the present invention, the photon source 350 maybe a vacuum UV lamp configured to generate ultraviolet radiation havinga wavelength of less than 200 nm, and is configured to generate anddirect photons into the intervening space 345 at the molecules that passthrough the exit orifice 320 d of the vaporizer 310. As previouslydiscussed, the photon source 350 may be situated generally opposite toan inlet orifice 217 of a second passageway 222, positioned to one side(e.g., not opposite) of the inlet orifice 217, or located almostanywhere on a sphere surrounding inlet orifice 217 (with due regard forother structures such as the vaporizer 310, but so as to still furnishphotons that intersect the vaporized sample in the intervening space345. Preferably, the photon source 350 is situated such that the photonsintersect the vaporized sample in the intervening space 345approximately in front of the inlet orifice 217 of second passageway222, and is placed relatively close to the ionization area to maximizethe photon flux and ionization rate.

[0072] According to the example embodiment illustrated in FIG. 7, adrying gas source (not shown) provides a stream of drying gas 351 acrossphoton source 350 in order to prevent build-up on photon source 350.This build-up may result from exposure to contaminants such as thesolvent, buffers, sample, etc. This contamination can over time build upon the lens, causing a loss in UV transmission and a decline inionization efficiency. It may also lead to noise or spurious background.One type of gas that may be employed is dry nitrogen, although othergases may also be employed. Advantageously, the gas that is employed asthe photon source drying gas stream 351 is the same as the gas employedas the nebulizer gas, thereby eliminating the requirement to employ morethan one kind of gas in the apparatus. In addition, the stream of dryinggas 351 may be maintained at a relatively high temperature, up to about300° C., more usually about 100° C., in order to more effectively reducethe likelihood of condensation on the lamp.

[0073] In the embodiment shown in FIG. 7, an electrically conductivehousing 216 having a housing opening 221 is positioned such that housingopening 221 is adjacent to the first passageway exit 320 d of firstpassageway 320. A second passageway 222, such as a capillary tube of amass spectrometer, is arranged within the housing 216 adjacent to thehousing opening 221. The second passageway 222 has an inlet orifice 217,a center axis 222 a, and an exit orifice 222 b which may be, asmentioned previously, connected to or exit into a mass spectrometer. Aspreviously mentioned, the term “passageway”, as used herein means “ionguide” in any form whatsoever. The center axis 320 b of the firstpassageway 320 can be substantially orthogonal relative to the centeraxis 222 a of the second passageway 222. More generally, the center axis320 b of the first passageway 320 and the center axis 222 a of thesecond passageway 222 define an angle therebetween that is in the rangeof about 20 degrees to 180 degrees.

[0074]FIG. 7 also illustrates a means for generating an electric fieldthat is employed to direct the ionized molecules from the interveningspace 345 into the inlet orifice 217 of the second passageway 222. Aspreviously discussed in connection with FIG. 6, there are many possibleconfigurations by which an electric field may be established, e.g.,generated and shaped, in order that ionized molecules are directedtowards the inlet orifice 217 of the second passageway 222. In theembodiment illustrated in FIG. 7, the electric field means includes afirst voltage source 303 and a second voltage source 304. The firstvoltage source 303 is coupled to the housing 216 and the second voltagesupply source 304 is coupled to the second passageway 222, such that afield is generated to direct the ionized molecules from the interveningspace 345 into the inlet orifice 217 of the second passageway 222.Again, as previously discussed, the means for generating the electricfield is not limited to a pair of voltage sources coupled to respectiveelectrodes, but may include any conceivable arrangement that is capableof generating an electric field for directing ionized molecules from theintervening space 345 into the inlet orifice 217 of the secondpassageway 222, e.g., electrodes in various configurations coupled toone or more voltage sources or coupled to or maintained substantially atground, e.g., at ground or near ground. In still another exampleembodiment, an additional electrode, which may be the housing 216, ispositioned between the inlet orifice of the second passageway and theother electrodes. Advantageously, this additional electrode has avoltage that differs from the voltage of the second passageway by about500 volts. The positioning of this additional electrode between theinlet orifice of the second passageway and the other electrodes permitsa small amount of heated drying gas 220 to be directed in front of theinlet orifice of the second passageway. The use of this heated dryinggas in this embodiment helps to reduce the amount of noise experiencedby the system without affecting the signal.

[0075] The present invention, according to another example embodimentthereof, may also employ dopants in order to help facilitate theionization of an analyte. FIG. 8 illustrates an apparatus 400 configuredaccording to one example embodiment of the present invention. In thisembodiment, a nebulizer 402 is configured to receive via its inlet aliquid sample solution 401, and to also receive via another inlet adopant 403 via a syringe pump 404. It is noted that this is merely onepossible method of introducing dopant into the system, and that anyconceivable method of doing so is contemplated by the present invention.

[0076] As previously mentioned, the apparatus may also comprise a dryinggas source (not shown) which provides a stream of drying gas 451 acrossphoton source 450 in order to prevent build-up on the photon source 450that may result from exposure to contaminants such as the solvent,buffers, sample, etc., and that may cause a loss in UV transmission, adecline in ionization efficiency or noise. FIG. 8 illustrates onepossible configuration of the drying gas stream, whereby the floworientation of the stream of drying gas 451 is 360° degrees around thecircumference of photon source 450 (thereby blowing radially across thelens toward its center and turning toward the ionization region). Forthis orientation of drying gas stream 451, it is preferable to maintainthe flow velocity and volume low, so as to leave the flow in theionization region relatively slow and stable. As previously explained,the stream of drying gas 451 may be maintained at a relatively hightemperature in order to reduce the humidity and thus the likelihood ofcondensation on the lamp.

[0077] In operation, according to this embodiment of the presentinvention, a liquid sample solution 401, which is comprised of asolvent, the dopant and an analyte, is nebulized so as to form anaerosol, and the resultant aerosol droplets, which also comprise thesolvent, the dopant and the analyte, proceed through the vaporizer. Theaerosol is heated in order to promote vaporization of the aerosol. Thevapor molecules exiting from the vaporized are subjected to photonsgenerated by the photon source 450. The interaction of the photons fromthe photon source 450 with the vapor molecules causes ionization of thedopant molecules. Then, subsequent collisions between the ionized dopantand the analyte, either directly or indirectly, result in ionization ofthe analyte. (In some embodiments, a separate dopant is not used and thesolvent performs the role as described here for the dopant.) Onceformed, the analyte ions are moved and directed by an electric fieldgenerating means towards and into the inlet orifice 417 of the secondpassageway 422.

[0078] In some embodiments, the motion of the analyte ions toward theinlet orifice of the second passageway may be assisted by gas flow. Forexample, an optional gas nozzle 652 is shown in FIG. 10. Gas isintroduced through the nozzle and directed toward the ions such as tosteer them toward the inlet orifice 617 of the second passageway 622. Atypical gas nozzle 652 in this application could have an inner diameterof about 0.5 mm through which a stream of dry nitrogen, for example, isflowed at a rate of about 0.2 to about 1 l/min. Gas flow introductioncan also be accomplished with other configurations, for example, anarray of gas nozzles. In some embodiments using a gas flow means formoving ions toward the inlet orifice 617, the gas nozzle can also be anelectrode, with a voltage applied to it such that an electric field isgenerated that also assists the motion of the ions into the inletorifice. Thus the means for moving ions into the inlet orifice cancomprise an electric field, or a gas flow, or a combination of anelectric field and a gas flow. In the embodiments where the meanscomprises such a combination, the gas nozzle, for example, need not bean electrode, i.e., it need not participate in the electric field means.One feature of using gas flow to assist ion motion is that it can aid indesolvation of any residual droplets.

[0079] All embodiments of the invention can be used with a mass analyzerin a mass spectrometer system. For example, FIG. 11 illustrates such amass spectrometer system 1. The atmospheric pressure ion source 2comprises a vaporizer 110 and a passageway 22 in substantiallyorthogonal configuration. A photon source 150 forms ions byphotoionization from vapor molecules exiting the vaporizer 110, and theions are directed into the passageway 22 by a means not illustrated inthe figure but as described above. Ions exit passageway 22 into achamber 3 that may comprise one or more vacuum chambers. Ions aretransported through an ion transport system 4 that may comprise ionoptics such as ion guides and lenses, and then into a mass analyzer 4.Mass analyzer 4 includes an ion detector and may be any of the kinds ofmass analyzers known in the art, e.g., quadrupole mass filter,time-of-flight, ion trap, ion cyclotron resonance (ICR) spectrometer,etc. If chamber 3 is at substantially atmospheric pressure, the massanalyzer can be an ion mobility mass spectrometer, for example. The iondetector in mass analyzer 1 is connected to a data acquisition oranalysis system 6.

[0080] The present invention provides the capability of ionizingeffluent from separation devices such as conventional high performanceliquid chromatography or capillary electrophoresis at various flowrates. The invention further provides that analyte ions are separatedfrom comparatively large volumes of vaporized aerosol from the columneffluent, and then, while keeping out as much of the aerosol aspossible, introducing the analyte ions into the vacuum system for massdetection and analysis. The invention provides the capability ofseparating analyte ions from the large volumes of vapor and directingthe analyte ions from the ionization chamber (typically operating atatmospheric pressure) to the mass spectrometer (MS) (typically operatingat 10⁻⁶ to 10⁻⁴ torr). The inventive separation capability preservesinstrument sensitivity because the maximum amount of analyte ions isintroduced into the vacuum system to be mass analyzed and detected.There is no reason other than convenience that the ion source needs tobe at atmospheric pressure; the invention can be practiced with ionsource pressures higher (e.g., about 2 atmospheres) or lower (a partialvacuum such as about 100 torr) than atmospheric. Specific pressuresquoted are not intended to be limiting, and higher or lower pressuresare considered to be within the scope of the invention. Similarly, theion source can be flooded with particular gases such as nitrogen, orargon, or helium, etc., in some embodiments, for example to enhancephoton transport or to aid in desolvation or ion formation by secondaryprocesses.

[0081] With respect to the atmospheric pressure photoionizationtechnique, substantially orthogonal ion sampling according to thepresent invention allows more efficient collection of the analyte byspraying the analyte ions past a sampling orifice, while directing thesolvent vapor and solvated droplets in the aerosol away from the ionsampling orifice such that they do not enter the vacuum system.

[0082] With respect to the atmospheric pressure photoionizationtechnique, the configuration described herein preserves instrumentsensitivity because the maximum amount of analyte ions is introducedinto the vacuum system to be mass analyzed and detected, but incompletesolvent-to-vapor phase change in the heater does not appear as noise, incontrast to the situation with the straight-on configurations of theprior art. Furthermore, the inventive sensitivity is preserved withoutoverwhelming the vacuum system with large volumes of liquid droplets orvapor and residual liquid-phase solvent.

[0083] The noise level in an apparatus configured according to thepresent invention is reduced relative to current systems, resulting inincreased signal relative to noise, and hence achieving greatersensitivity. Performance is simplified and the system is more robustbecause optimization of the position of the first passageway, gas flowand voltages show less sensitivity to small changes. The simplifiedperformance and reduced need for optimization also result in a systemless dependent upon flow rate and mobile phase conditions. The reducedneed for optimization extends to changing mobile phase flow rates andproportions. Practically speaking, this means that an apparatusconfigured to employ the inventive system can be run under a variety ofconditions without adjustment.

[0084] Thus, the several aforementioned objects and advantages of thepresent invention are most effectively attained. Those skilled in theart will appreciate that numerous modifications of the exemplaryembodiment described hereinabove may be made without departing from thespirit and scope of the invention. Although a single exemplaryembodiment of the present invention has been described and disclosed indetail herein, it should be understood that this invention is in nosense limited thereby and that its scope is to be determined by that ofthe appended claims.

What is claimed is:
 1. An atmospheric pressure ion source, comprising: avaporizer with a center axis; a photon source adjacent said vaporizerfor creating ions from vapor molecules exiting the vaporizer; apassageway adjacent said vaporizer and having a center axis, said centeraxis of said vaporizer and said center axis of said passageway definingan angle therebetween that is in the range of about 20 to 180 degrees;and a means interposed between the vaporizer and the passageway fordirecting the ions into the passageway.
 2. The atmospheric pressure ionsource of claim 1, wherein the photon source comprises an ultraviolet(UV) lamp.
 3. The atmospheric pressure ion source of claim 1, furthercomprising a housing that substantially encloses the passageway and thathas an opening adjacent to the center axis of the passageway.
 4. Theatmospheric pressure ion source of claim 3, wherein the housing is atsubstantially ground potential.
 5. The atmospheric pressure ion sourceof claim 1, wherein the means for directing the ions into the passagewaycomprises an electric field.
 6. The atmospheric pressure ion source ofclaim 5, wherein a source of the electric field comprises a voltageapplied to an electrode.
 7. The atmospheric pressure ion source of claim6, wherein the vaporizer comprises said electrode.
 8. The atmosphericpressure ion source of claim 6, wherein the passageway comprises saidelectrode.
 9. The atmospheric pressure ion source of claim 6, whereinthe photon source comprises said electrode.
 10. The atmospheric pressureion source of claim 6, further comprising a housing that substantiallyencloses the passageway, that has an opening adjacent to the centralaxis of the passageway and that comprises said electrode.
 11. Theatmospheric pressure ion source of claim 1, wherein the means fordirecting the ions into the passageway comprises a flow of gas.
 12. Theatmospheric pressure ion source of claim 1, wherein the means fordirecting the ions into the passageway comprises a gas nozzle.
 13. Theatmospheric pressure ion source of claim 12, wherein a voltage isapplied to the gas nozzle.
 14. The atmospheric pressure ion source ofclaim 12, wherein the gas nozzle is at about ground potential.
 15. Theatmospheric pressure ion source of claim 1, further comprising a meansfor creating a flow of gas across a portion of the photon source. 16.The atmospheric pressure ion source of claim 15, wherein the gas isnitrogen.
 17. The atmospheric pressure ion source of claim 1, whereinthe photon source surrounds the vapor molecules exiting the vaporizer.18. A mass spectrometer system comprising: an atmospheric pressure ionsource comprising a vaporizer with a center axis; a photon sourceadjacent said vaporizer for creating ions from vapor molecules exitingthe vaporizer; a passageway adjacent said vaporizer and having a centeraxis, said center axis of said vaporizer and said center axis of saidpassageway defining an angle therebetween that is in the range of about20 to 180 degrees; and a means interposed between the vaporizer and thepassageway for directing the ions into the passageway; and a massanalyzer coupled to the atmospheric pressure ion source such that ionstraveling through the passageway are transported into the mass analyzer.19. A method for supplying ions to a mass spectrometer, comprising:directing a stream of vaporized molecules approximately along amolecular axis; irradiating the stream of vaporized molecules withphotons to produce the ions; and moving the ions into a passagewayhaving a center axis, wherein the molecular axis and the center axis ofthe passageway define an angle in the range of about 20 to 180 degrees.20. The method for supplying ions to a mass spectrometer of claim 19,wherein the range of the angle is about 80 to about 100 degrees.
 21. Themethod for supplying ions to a mass spectrometer of claim 19, whereinthe molecular axis and the center axis of the passageway do notintersect to define said angle.
 22. A method for analyzing ions,comprising directing a stream of vaporized molecules approximately alonga molecular axis; irradiating the stream of vaporized molecules withphotons to produce the ions; and moving the ions into a passagewayhaving a center axis, wherein the molecular axis and the center axis ofthe passageway define an angle in the range of about 20 to 180 degrees;and measuring the mass to charge ratios of the ions.
 23. The method foranalyzing ions of claim 22, wherein the range of the angle is about 80to about 100 degrees.
 24. The method for analyzing ions of claim 22,wherein the molecular axis and the center axis of the passageway do notintersect to define said angle.
 25. A method for creating andtransporting ions in an atmospheric pressure ion source, comprising:photoionizing a stream of vaporized molecules directed approximatelyalong a molecular axis; and moving ions so created along a central axisof a passageway, wherein said central axis and the molecular axis definean angle in the range of about 20 to 180 degrees.
 26. The method ofclaim 25, wherein the range of the angle is about 80 to about 100degrees.